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EVP_EncryptInit(3)

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NAME    [Toc]    [Back]

       EVP_EncryptInit,    EVP_EncryptUpdate,   EVP_EncryptFinal,
       EVP_DecryptInit,   EVP_DecryptUpdate,    EVP_DecryptFinal,
       EVP_CipherInit,     EVP_CipherUpdate,     EVP_CipherFinal,
       EVP_CIPHER_CTX_set_key_length,        EVP_CIPHER_CTX_ctrl,
       EVP_CIPHER_CTX_cleanup,              EVP_get_cipherbyname,
       EVP_get_cipherbynid, EVP_get_cipherbyobj,  EVP_CIPHER_nid,
       EVP_CIPHER_block_size,              EVP_CIPHER_key_length,
       EVP_CIPHER_iv_length,  EVP_CIPHER_flags,  EVP_CIPHER_mode,
       EVP_CIPHER_type,                    EVP_CIPHER_CTX_cipher,
       EVP_CIPHER_CTX_nid,             EVP_CIPHER_CTX_block_size,
       EVP_CIPHER_CTX_key_length,       EVP_CIPHER_CTX_iv_length,
       EVP_CIPHER_CTX_get_app_data,  EVP_CIPHER_CTX_set_app_data,
       EVP_CIPHER_CTX_type,                 EVP_CIPHER_CTX_flags,
       EVP_CIPHER_CTX_mode,             EVP_CIPHER_param_to_asn1,
       EVP_CIPHER_asn1_to_param - EVP cipher routines

SYNOPSIS    [Toc]    [Back]

       #include <openssl/evp.h>

       int EVP_EncryptInit(
               EVP_CIPHER_CTX   *ctx,   const  EVP_CIPHER  *type,
       unsigned char *key, unsigned char *iv );  int  EVP_EncryptUpdate(

               EVP_CIPHER_CTX    *ctx,    unsigned   char   *out,
       int *outl, unsigned char *in, int inl ); int  EVP_EncryptFinal(

               EVP_CIPHER_CTX    *ctx,    unsigned   char   *out,
       int *outl ); int EVP_DecryptInit(
               EVP_CIPHER_CTX  *ctx,  const   EVP_CIPHER   *type,
       unsigned  char  *key, unsigned char *iv ); int EVP_DecryptUpdate(

               EVP_CIPHER_CTX   *ctx,   unsigned    char    *out,
       int  *outl, unsigned char *in, int inl ); int EVP_DecryptFinal(

               EVP_CIPHER_CTX   *ctx,   unsigned   char    *outm,
       int *outl ); int EVP_CipherInit(
               EVP_CIPHER_CTX   *ctx,   const  EVP_CIPHER  *type,
       unsigned char *key, unsigned char  *iv,  int  enc  );  int
       EVP_CipherUpdate(
               EVP_CIPHER_CTX    *ctx,    unsigned   char   *out,
       int *outl, unsigned char *in, int inl ); int EVP_CipherFinal(

               EVP_CIPHER_CTX    *ctx,   unsigned   char   *outm,
       int *outl ); int EVP_CIPHER_CTX_set_key_length(
               EVP_CIPHER_CTX   *x,    int    keylen    );    int
       EVP_CIPHER_CTX_ctrl(
               EVP_CIPHER_CTX  *ctx, int type, int arg, void *ptr
       ); int EVP_CIPHER_CTX_cleanup(
               EVP_CIPHER_CTX    *a    );    const     EVP_CIPHER
       *EVP_get_cipherbyname(
               const char *name ); #define EVP_get_cipherbynid(a)
       EVP_get_cipherbyname(OBJ_nid2sn(a))                #define
       EVP_get_cipherbyobj(a) EVP_get_cipherbynid(OBJ_obj2nid(a))

       #define   EVP_CIPHER_nid(e)          ((e)->nid)    #define
       EVP_CIPHER_block_size(e)   ((e)->block_size)       #define
       EVP_CIPHER_key_length(e)   ((e)->key_len)          #define
       EVP_CIPHER_iv_length(e)         ((e)->iv_len)      #define
       EVP_CIPHER_flags(e)        ((e)->flags)            #define
       EVP_CIPHER_mode(e)         ((e)->flags) & EVP_CIPH_MODE)

       int EVP_CIPHER_type(
               const      EVP_CIPHER      *ctx     );     #define
       EVP_CIPHER_CTX_cipher(e)   ((e)->cipher)           #define
       EVP_CIPHER_CTX_nid(e)      ((e)->cipher->nid)      #define
       EVP_CIPHER_CTX_block_size(e)    ((e)->cipher->block_size)
       #define    EVP_CIPHER_CTX_key_length(e)     ((e)->key_len)
       #define
       EVP_CIPHER_CTX_iv_length(e)   ((e)->cipher->iv_len)
       #define   EVP_CIPHER_CTX_get_app_data(e)   ((e)->app_data)
       #define                   EVP_CIPHER_CTX_set_app_data(e,d)
       ((e)->app_data=(char *)(d)) #define EVP_CIPHER_CTX_type(c)
       EVP_CIPHER_type(EVP_CIPHER_CTX_cipher(c))          #define
       EVP_CIPHER_CTX_flags(e)         ((e)->cipher->flags)
       #define  EVP_CIPHER_CTX_mode(e)      ((e)->cipher->flags &
       EVP_CIPH_MODE)

       int EVP_CIPHER_param_to_asn1(
               EVP_CIPHER_CTX  *c,   ASN1_TYPE   *type   );   int
       EVP_CIPHER_asn1_to_param(
               EVP_CIPHER_CTX *c, ASN1_TYPE *type );

DESCRIPTION    [Toc]    [Back]

       The EVP cipher routines are a high level interface to certain
 symmetric ciphers.

       The EVP_EncryptInit() function initializes a  cipher  context
  ctx  for  encryption  with cipher type.  The type is
       usually supplied by a function such  as  EVP_des_cbc().The
       key  is  the symmetric key to use, and iv is the IV to use
       (if necessary). The actual number of bytes  used  for  the
       key  and  IV  depends on the cipher. It is possible to set
       all parameters to NULL except type in an initial call  and
       supply  the  remaining parameters in subsequent calls, all
       of which have type set to NULL.  This  is  done  when  the
       default cipher parameters are not appropriate.

       The  EVP_EncryptUpdate()  function encrypts inl bytes from
       the buffer in and writes the  encrypted  version  to  out.
       This function can be called multiple times to encrypt successive
 blocks of data. The amount of data written depends
       on the block alignment of the encrypted data. As a result,
       the amount of data written may be anything from zero bytes
       to  (inl  + cipher_block_size - 1); so outl should contain
       sufficient room.  The actual number of  bytes  written  is
       placed in outl.

       The  EVP_EncryptFinal()  function encrypts the final data,
       that is any data that remains in a partial block. It  uses
       standard block padding (PKCS padding). The encrypted final
       data is written to out which should have sufficient  space
       for  one  cipher  block.  The  number  of bytes written is
       placed in outl.  After this function is called the encryption
  operation  is  finished  and  no  further  calls  to
       EVP_EncryptUpdate() should be made.

       The    EVP_DecryptInit(),     EVP_DecryptUpdate(),     and
       EVP_DecryptFinal() functions are the corresponding decryption
  operations.  The  EVP_DecryptFinal()  function  will
       return  an  error code if the final block is not formatted
       correctly. The parameters and restrictions  are  identical
       to  the  encryption  operations  except that the decrypted
       data buffer out passed to EVP_DecryptUpdate() should  have
       sufficient room for (inl + cipher_block_size) bytes unless
       the cipher block size is 1 in which case inl bytes is sufficient.


       The  EVP_CipherInit(), EVP_CipherUpdate(), and EVP_CipherFinal()functions
 can be used for decryption or encryption.
       The  operation  performed  depends on the value of the enc
       parameter. It should be set to 1  for  encryption,  0  for
       decryption and -1 to leave the value unchanged (the actual
       value of enc being supplied in a previous call).

       The EVP_CIPHER_CTX_cleanup() function clears all  information
  from a cipher context. It should be called after all
       operations using a cipher are complete so sensitive information
 does not remain in memory.

       The   EVP_get_cipherbyname(),  EVP_get_cipherbynid(),  and
       EVP_get_cipherbyobj()  functions  return   an   EVP_CIPHER
       structure   when  passed  a  cipher  name,  a  NID  or  an
       ASN1_OBJECT structure.

       The EVP_CIPHER_nid()  and  EVP_CIPHER_CTX_nid()  functions
       return  the  NID  of a cipher when passed an EVP_CIPHER or
       EVP_CIPHER_CTX structure.  The  actual  NID  value  is  an
       internal  value  which may not have a corresponding OBJECT
       IDENTIFIER.

       The              EVP_CIPHER_key_length()               and
       EVP_CIPHER_CTX_key_length() function return the key length
       of a cipher when passed an  EVP_CIPHER  or  EVP_CIPHER_CTX
       structure.  The constant EVP_MAX_KEY_LENGTH is the maximum
       key    length    for    all    ciphers.    Although    the
       EVP_CIPHER_key_length()  function  is  fixed  for  a given
       cipher, the value of the EVP_CIPHER_CTX_key_length() function
 may be different for variable key length ciphers.

       The  EVP_CIPHER_CTX_set_key_length() function sets the key
       length of the cipher ctx. If the cipher is a fixed  length
       cipher  then attempting to set the key length to any value
       other than the fixed value is an error.

       The EVP_CIPHER_iv_length() and  EVP_CIPHER_CTX_iv_length()
       functions  return the IV length of a cipher when passed an
       EVP_CIPHER or EVP_CIPHER_CTX. It will return zero  if  the
       cipher does not use an IV.  The constant EVP_MAX_IV_LENGTH
       is the maximum IV length for all ciphers.

       The              EVP_CIPHER_block_size()               and
       EVP_CIPHER_CTX_block_size()  functions  return  the  block
       size  of  a  cipher   when   passed   an   EVP_CIPHER   or
       EVP_CIPHER_CTX  structure.  The constant EVP_MAX_IV_LENGTH
       is also the maximum block length for all ciphers.

       The EVP_CIPHER_type() and EVP_CIPHER_CTX_type()  functions
       return the type of the passed cipher or context. This type
       is the actual NID of  the  cipher  OBJECT  IDENTIFIER.  As
       such, it ignores the cipher parameters. and 40 bit RC2 and
       128 bit RC2 have the same NID. If the cipher does not have
       an  object  identifier  or does not have ASN1 support this
       function will return NID_undef.

       The   EVP_CIPHER_CTX_cipher()   function    returns    the
       EVP_CIPHER  structure when passed an EVP_CIPHER_CTX structure.


       The EVP_CIPHER_mode() and EVP_CIPHER_CTX_mode()  functions
       return   the   block   cipher   mode:   EVP_CIPH_ECB_MODE,
       EVP_CIPH_CBC_MODE,          EVP_CIPH_CFB_MODE,          or
       EVP_CIPH_OFB_MODE.  If  the cipher is a stream cipher then
       EVP_CIPH_STREAM_CIPHER is returned.

       The EVP_CIPHER_param_to_asn1() function sets the AlgorithmIdentifier
  parameter  based  on  the passed cipher. This
       typically will include  any  parameters  and  an  IV.  The
       cipher  IV  (if  any)  must be set when this call is made.
       This call should be made before  the  cipher  is  actually
       used  (before  any  EVP_EncryptUpdate()  or EVP_DecryptUpdate()
 calls, for example). This function may fail if  the
       cipher does not have any ASN1 support.

       The  EVP_CIPHER_asn1_to_param()  function  sets the cipher
       parameters based on an ASN1 AlgorithmIdentifier parameter.
       The  precise  effect  depends on the cipher In the case of
       RC2, for example, it will set the  IV  and  effective  key
       length.  This  function  should  be  called after the base
       cipher type is set but before the key is set. For example,
       the  EVP_CipherInit()  function will be called with the IV
       and key set to NULL. The EVP_CIPHER_asn1_to_param()  function
 will be called and finally the EVP_CipherInit() function.
 All parameters except the key are set to NULL. It is
       possible  for this function to fail if the cipher does not
       have any ASN1 support or the parameters cannot be set (for
       example the RC2 effective key length is not supported).

       The  EVP_CIPHER_CTX_ctrl()  function allows various cipher
       specific parameters to be determined  and  set.  Currently
       only the RC2 effective key length and the number of rounds
       of RC5 can be set.

   Cipher Listing    [Toc]    [Back]
       All algorithms have a fixed key  length  unless  otherwise
       stated.   Null cipher: does nothing.  DES in CBC, ECB, CFB
       and OFB modes respectively.  Two key triple  DES  in  CBC,
       ECB, CFB and OFB modes respectively.  Three key triple DES
       in CBC, ECB, CFB and OFB modes respectively.   DESX  algorithm
 in CBC mode.  RC4 stream cipher.  This is a variable
       key length cipher with default key length 128  bits.   RC4
       stream cipher with 40 bit key length. This is obsolete and
       new    code    should    use    the    EVP_rc4()and    the
       EVP_CIPHER_CTX_set_key_length()  functions.   IDEA encryption
 algorithm in CBC, ECB,  CFB  and  OFB  modes  respectively.
  RC2 encryption algorithm in CBC, ECB, CFB and OFB
       modes respectively. This is a variable key  length  cipher
       with  an additional parameter called effective key bits or
       effective key length. By default both are set to 128 bits.
       RC2  algorithm  in  CBC mode with a default key length and
       effective key length of 40 and 64 bits. These are obsolete
       and    new    code    should    use   the   EVP_rc2_cbc(),
       EVP_CIPHER_CTX_set_key_length(), and EVP_CIPHER_CTX_ctrl()
       functions  to set the key length and effective key length.
       Blowfish encryption algorithm in CBC,  ECB,  CFB  and  OFB
       modes  respectively. This is a variable key length cipher.
       CAST encryption algorithm in CBC, ECB, CFB and  OFB  modes
       respectively.  This  is a variable key length cipher.  RC5
       encryption algorithm  in  CBC,  ECB,  CFB  and  OFB  modes
       respectively. This is a variable key length cipher with an
       additional "number of rounds parameter. By default the key
       length is set to 128 bits and 12 rounds.








NOTES    [Toc]    [Back]

       Where  possible  the  EVP  interface  to symmetric ciphers
       should be used in preference to the low level  interfaces.
       This  is  because the code then becomes transparent to the
       cipher used and much more flexible.

       PKCS padding works by adding n padding bytes of value n to
       make the total  length of the encrypted data a multiple of
       the block size. Padding is always added so if the data  is
       already  a  multiple  of  the  block size n will equal the
       block size. For example, if the block size  is  8  and  11
       bytes  are to be encrypted then 5 padding bytes of value 5
       will be added.

       When decrypting, the final block is checked to see  if  it
       has the correct form.

       Although the decryption operation can produce an error, it
       is not a strong test that the input data or  key  is  correct.
 A random block has better than a 1-in- 256 chance of
       being of the correct format. Problems with the input  data
       earlier on will not produce a final decrypt error.

       The EVP_EncryptInit(), EVP_EncryptUpdate(), EVP_EncryptFinal(),
       EVP_DecryptInit(),       EVP_DecryptUpdate(),
       EVP_CipherInit(),          EVP_CipherUpdate(),         and
       EVP_CIPHER_CTX_cleanup() functions did not  return  errors
       in  OpenSSL version 0.9.5a or earlier.  Software only versions
 of encryption algorithms  will  never  return  error
       codes  for  these functions, unless there is a programming
       error (for example, an attempt to set the key  before  the
       cipher is set in EVP_EncryptInit()).

RESTRICTIONS    [Toc]    [Back]

       For  RC5  the number of rounds can be set only to 8, 12 or
       16. This is a limitation of the current  RC5  code  rather
       than the EVP interface.

       It is not possible to disable PKCS padding.

       EVP_MAX_KEY_LENGTH and EVP_MAX_IV_LENGTH only refer to the
       internal ciphers  with  default  key  lengths.  If  custom
       ciphers exceed these values the results are unpredictable.
       This is because it has become standard practice to  define
       a   generic  key as a fixed unsigned char array containing
       EVP_MAX_KEY_LENGTH bytes.

       The ASN1 code is incomplete (and sometimes inaccurate). It
       has  only  been  tested  for certain common S/MIME ciphers
       (RC2, DES, triple DES) in CBC mode.

RETURN VALUES    [Toc]    [Back]

       The    EVP_EncryptInit(),     EVP_EncryptUpdate(),     and
       EVP_EncryptFinal()  functions  return  1 for success and 0
       for failure.

       The EVP_DecryptInit()  and  EVP_DecryptUpdate()  functions
       return 1 for success and 0 for failure. The EVP_DecryptFinal()
 function returns 0 if the decrypt failed  or  1  for
       success.

       The   EVP_CipherInit()  and  EVP_CipherUpdate()  functions
       return 1 for success and 0 for failure.

       The EVP_CipherFinal() function returns 0 for a  decryption
       failure or 1 for success.

       The  EVP_CIPHER_CTX_cleanup()  function returns 1 for success
 and 0 for failure.

       The  EVP_get_cipherbyname(),  EVP_get_cipherbynid(),   and
       EVP_get_cipherbyobj()   functions   return  an  EVP_CIPHER
       structure or NULL on error.

       The EVP_CIPHER_nid()  and  EVP_CIPHER_CTX_nid()  functions
       return a NID.

       The               EVP_CIPHER_block_size()              and
       EVP_CIPHER_CTX_block_size()  functions  return  the  block
       size.

       The               EVP_CIPHER_key_length()              and
       EVP_CIPHER_CTX_key_length()  functions  return   the   key
       length.

       The  EVP_CIPHER_iv_length() and EVP_CIPHER_CTX_iv_length()
       functions return the IV length or zero if the cipher  does
       not use an IV.

       The  EVP_CIPHER_type() and EVP_CIPHER_CTX_type() functions
       return the  NID  of  the  cipher's  OBJECT  IDENTIFIER  or
       NID_undef if it has no defined OBJECT IDENTIFIER.

       The EVP_CIPHER_CTX_cipher() function returns an EVP_CIPHER
       structure.

       The             EVP_CIPHER_param_to_asn1()             and
       EVP_CIPHER_asn1_to_param() functions return 1 for  success
       or zero for failure.

EXAMPLES    [Toc]    [Back]

       Get the number of rounds used in RC5:
        int nrounds;
        EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GET_RC5_ROUNDS, 0, &i);

       Get the RC2 effective key length:
        int key_bits;
        EVP_CIPHER_CTX_ctrl(ctx,   EVP_CTRL_GET_RC2_KEY_BITS,  0,
       &i);

       Set the number of rounds used in RC5:
        int nrounds;
        EVP_CIPHER_CTX_ctrl(ctx,   EVP_CTRL_SET_RC5_ROUNDS,    i,
       NULL);

       Set the number of rounds used in RC2:
        int nrounds;
        EVP_CIPHER_CTX_ctrl(ctx,   EVP_CTRL_SET_RC2_KEY_BITS,  i,
       NULL);

SEE ALSO    [Toc]    [Back]

      
      
       Functions: evp(3)



                                               EVP_EncryptInit(3)
[ Back ]
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